'LIB ERROR: object lost from scene' error when opening file
I can't say why this has happened, but your tunnel is still in the file.

Make a duplicate of the 'ROAD' object, go to the duplicate 'ROAD's Data panel, and then select the data that has a '0' next to it:



This should assign the mesh datablock back to an object and your duplicate road should now be your tunnel. The '0' next to the mesh datablock meant that the mesh wasn't being used (as it wasn't assigned to any object). 

From what I've read about the error you got it refers to objects that were linked from other files, and then the object in the original file has been renamed, breaking the link, meaning blender is unable to find and load the object. 

However, there are some reports of this happening without any renaming, which if you are able to reproduce it, should be reported as a bug report here (or added to that bug report I linked to).